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1

Evaluation of the Ruttenber Database for Impact on 

Rocky Flats Special Exposure Cohort Eligibility 

Brant Ulsh, Ph.D., CHP, and Jim Neton, Ph.D., CHP 

National Institute for Occupational Safety and Health 

Office of Compensation Analysis and Support 

July 2009
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Summary

In August 2007, the Secretary of the Department of Health and Human Services designated two 

classes of employees from the Rocky Flats Plant (RFP) for inclusion in the Special Exposure 

Cohort (SEC). Since that time, there has been a great deal of inquiry as to whether the use of 

data in epidemiological studies authored by A. James Ruttenber, Margaret Ruttenber, and their 

colleagues, as opposed to data from the Neutron Dose Reconstruction Project (NDRP), would 

result in the inclusion of a great number of workers from RFP in the SEC. Much of the 

speculation and attention surrounding the Ruttenber data has been driven by the print media. The 

Rocky Mountain News (RMN) has published numerous articles that question the validity of 

relying on the Department of Energy’s NDRP data (versus the Ruttenber data) to determine 

eligibility for the RFP SEC [1-6]. This report summarizes the NIOSH evaluation and findings of 

the comparison of these two data sets (Ruttenber and NDRP). Copies of this report have been 

distributed to the ABRWH, the SEC Petitioners, and publicly displayed on the NIOSH website. 

Although media reports have alleged that the data NIOSH uses for dose reconstruction of Rocky 

Flats Plant (RFP) workers (i.e., the dosimetry records provided by the Department of Energy 

(DOE), including the (NDRP) are distinct, this is inaccurate. James Ruttenber served on the 

board advising the NDRP at the same time as he was conducting epidemiological studies with 

Margaret Ruttenber. Not surprisingly, there is considerable overlap between the two projects. In 

fact, the source dosimetry data used by both the NDRP and the Ruttenber studies were provided 

by the Rocky Flats site. 

The methods used by the Ruttenber team and the NDRP in the estimation of unmonitored 

neutron dose do differ somewhat. The Ruttenber team recognized that it would have been 

preferable to use the NDRP results in their work; however, the NDRP was not completed until 

several years after the Ruttenber studies. Since NDRP results were not available to the Ruttenber 

team, they had to devise methods to impute neutron doses from combined (neutron plus gamma) 

penetrating doses. It is here that differences in calculated neutron doses and to whom these 

doses were assigned arise, inconsequential as they are. 

In order to determine whether these differences would result in changes to any individuals’ SEC 

status, NIOSH assessed whether any RFP claimants had positive neutron dose recorded in the 

Ruttenber database that was not indicated in the NDRP. NIOSH has access to the dosimetry files 

for RFP claimants; therefore we queried the Ruttenber and NDRP databases to identify any 

individuals with positive neutron dose in the former, but not the latter, during the SEC period. 

We then determined whether or not the individuals had already been included in the SEC and, 

for those who had not, we applied the criteria for inclusion in the SEC employed by the 

Department of Labor (DOL) (e.g., at least 250 days of employment in the SEC period, having a 

qualifying cancer, and having at least 100 mrem of neutron exposure in any given year prior to 

1967). This allowed NIOSH to establish how large an impact use of the Ruttenber data (in 

addition to the NDRP data) would have on determining SEC eligibility. DOL is responsible for 

determining SEC eligibility. However, it is NIOSH’s belief that the use of the Ruttenber 

database in addition to the information already used by DOL might result in one additional 

member to the SEC. NIOSH is confident that this general pattern observed among RFP claimants 
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3

would be reflected in the worker population at large. Thus, NIOSH feels comfortable concluding 

that media claims that use of the Ruttenber data would result in upwards of 3,000 workers being 

added to the SEC are inaccurate. 

I. Background

This section provides an overview of (1) the NDRP; (2) the timeline that culminated in the 

issuance of the NDRP; and (3) the epidemiological studies conducted by the Ruttenber team at 

the Colorado Department of Public Health and the Environment (CDPHE). Articles appearing in 

the Rocky Mountain News (RMN) presented the data used by NIOSH for RFP dose 

reconstructions (i.e., DOE dosimetry records, including the NDRP) and the data used in the 

Ruttenbers’ studies as distinct [1-6]. This is inaccurate. In fact, Jim Ruttenber served on the 

advisory board for the NDRP and used the same source dosimetry data for his studies as were 

used by the NDRP. Not surprisingly, there is considerable interaction and overlap between the 

two projects. 

An informal medical monitoring program was established for former RFP workers in 1980; this 

program was formalized as the Medical Monitoring of Former Employees program, and funded 

by DOE’s Office of Occupational Medicine and Medical Surveillance in 1992 [7

]. It was 

recognized early in the history of the medical monitoring program that cooperation among 

ongoing epidemiological, beryllium, and radiological health programs would be beneficial [8]. 

The CDPHE submitted a grant application to NIOSH for support of an epidemiologic evaluation 

of RFP workers, with James Ruttenber as lead investigator, on August 9, 1993. The grant 

application was approved by NIOSH for a five-year contract period beginning September 30, 

1993 and ending September 29, 1998. The application acknowledged the MMFE program, 

described the collaboration between this program and the CDPHE, and proposed, “By working 

closely with this Rocky Flats program, the research team plans to promote the development of 

similar dosimetric techniques”. The application also recognized issues with past neutron dose 

estimates, however, and noted that addressing these issues would be “time-consuming and 

expensive”. Therefore, depending in part on DOE’s plans for historical dose reconstructions for 

the RFP workforce, it was proposed that, “the team will explore alternate approaches for making 

semi-quantitative estimates of radiation exposures and doses. The team will also explore the 

utility of job exposure matrices for exposure estimates that can be applied to the entire cohort”. 

The MMFE program was advised by the MMFE Advisory Committee (hereafter referred to as 

“the Committee”). The Committee included experts in health physics, radiation biology, 

medicine, epidemiology (including James Ruttenber, discussed later in this report), and neutron 

dosimetry [7

]. Although the program originally focused on internal doses received primarily as a 

result of intakes of plutonium, DOE requested that external dose, and specifically neutron dose, 

be considered [8

]. A former RFP Health Physicist, Roger Falk, identified the neutron dose 

estimates from the 1950s and 1960s as the weakest part of the external dosimetry estimates for 

former workers. In 1994, the Committee agreed with Mr. Falk’s recommendations that the 

neutron doses from the 1950s-60s should be re-evaluated, and the NDRP was launched as a 

subproject of the overall MMFE program [9

]. The Committee explicitly endorsed collaboration 
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4

between the NDRP and the ongoing epidemiological studies being conducted by Jim Ruttenber 

and his colleagues at the CDPHE [10;11]. A sub-committee devoted to oversight of the NDRP 

was established in 1995 [11]. In late 1995, the Committee decided that the NDRP should reevaluate neutron doses that had originally been improperly measured (i.e., re-read neutron films) 

and develop methodologies to determine unmonitored neutron doses. It was also in late 1995 

that concerns about resources available for the NDRP and the rest of the MMFE program began 

to be expressed [12]. These concerns continued into 1996 [13], and at the beginning of 1997, the 

Committee decided to discontinue advising the NDRP due to limited resources [14;15]. The 

Committee apparently reconsidered this decision, as the NDRP was again taken up in 1998 [16]; 

however, there was continuing concern over competition for resources [17;18]. By mid-2000, rereading of films was well underway, and the Committee began to consider how to translate the 

neutron track data into neutron dose estimates [19]; however, there were continuing resource 

concerns and doubts about whether the NDRP could be completed [20]. 

It was at this point in 2001, well prior to completion of the NDRP in 2005, that Dr. Ruttenber 

published two papers on his Rocky Flats research [21;22]. He reported to NIOSH on the 

CDPHE’s epidemiologic studies of Rocky Flats workers in 2003 [23]. It is important to note that 

since the NDRP was not yet complete, the CDPHE team had to devise strategies to estimate 

neutron doses (as discussed more completely later in this report). 

The NDRP apparently turned a corner in 2001, as the Committee recognized the excellent 

progress that was being made [24]. Around this time, the significant milestones of matching 

90,000 films to historical personnel records and re-reading approximately 2/3 of the films were 

completed [25]. It was also at this time that the Committee concluded that the NDRP “will 

clearly serve as a model for other DOE facilities and provide reliable dose estimates for workers 

under the Energy Employees Occupational Illness Compensation Act”. The NDRP was nearing 

completion by the end of November, 2003 [26], and the Committee issued its final 

recommendations in November, 2004 [27]. The Committee concluded that “The implementation 

of the dose reconstruction protocol and the statistical interpretation of results were developed 

using sound scientific methodology”. The Committee further recommended that “the neutron 

doses estimated by the NDRP be included in the final dose of record for affected workers at the 

Rocky Flats Plant”. The NDRP protocol was officially issued in 2005 [28], and the re-evaluated 

doses were released to NIOSH for use in dose reconstructions under EEOICPA at that time. 

On April 4, 2006, Brant Ulsh met with Jim Ruttenber to discuss the data that the latter had in his 

possession from his epidemiological studies at RFP. Dr. Ruttenber summarized the format of the 

data and the architecture of the database, and informed Dr. Ulsh of the sources of his data. 

According to Dr. Ruttenber, the dosimetry data was provided to him by the staff working on the 

NDRP. Dr. Ulsh determined that his data might be marginally useful to NIOSH as it provided 

job exposure histories, but NIOSH had a more complete dosimetry data set than did Dr. 

Ruttenber because NIOSH had access to the complete NDRP. NIOSH also later obtained the job 

history cards for individual workers from DOE that were captured and used in the NDRP. 

Access to this data diminished the usefulness of the Ruttenber job exposure history data, 

although the worker interviews might still be of marginal value to NIOSH, if they provided 

information not otherwise captured in NIOSH interviews. 
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5

During the evaluation of the RFP SEC petition, the Advisory Board on Radiation and Worker 

Health (ABRWH) engaged in considerable debate regarding what data sets were appropriate for 

use. Ultimately, the ABRWH did not accept the results of the NDRP as sufficient for use in 

dose-reconstruction prior to 1967, and recommended SEC classes as a result. The Secretary of 

Health and Human Services (HHS) received the Board’s recommendation regarding the RFP 

SEC petition and made the determination to add the following two classes of workers to the 

SEC: 

Employees of the Department of Energy (DOE), its predecessor agencies, or DOE 

contractors or subcontractors who were monitored or should have been monitored for 

neutron exposures while working at the Rocky Flats Plant in Golden, Colorado, for a 

number of work days aggregating at least 250 work days from April 1, 1952, through 

December 31, 1958, or in combination with work days within the parameters 

established for one or more other classes of employees in the Special Exposure 

Cohort. 

Employees of the Department of Energy (DOE), its predecessor agencies, or DOE 

contractors or subcontractors who were monitored or should have been monitored for 

neutron exposures while working at the Rocky Flats Plant in Golden, Colorado, for a 

number of work days aggregating at least 250 work days from January 1, 1959, 

through December 31, 1966, or in combination with work days within the parameters 

established for one or more other classes of employees in the Special Exposure 

Cohort. 

Because of the way in which these classes were defined, the identification of those workers with 

the potential for neutron exposure became a critical factor in establishing eligibility for 

compensation. Both NIOSH and the ABRWH continued to want to compare data from NDRP 

with that in the Ruttenber data sets to ensure that the data used by NIOSH for dose 

reconstructions and by DOL for determining membership in the SEC was complete. On April 

19, 2008, Brant Ulsh of NIOSH met with Margaret Ruttenber (Jim Ruttenber had passed away 

by this time) to discuss obtaining the Ruttenber data in their entirety, and to discuss ways to 

compare lists of workers with neutron exposure in her database against the NDRP. They 

discussed strategies to query her database, but agreed that a follow-up visit to collaboratively 

generate the appropriate lists of workers and to take possession of the Ruttenber data would be 

required. They also discussed the possibility that workers received neutron exposures in 

buildings other than those included in the SEC, as had been suggested by reports in the RMN [1-

6

]. Both Dr. Ulsh and Ms. Ruttenber agreed that this was a misinterpretation of the data. While 

workers may have been officially stationed in other buildings, their duties took them to buildings 

(included in the SEC) where they received neutron exposure. Dr. Ulsh stated, and still believes, 

that if workers had recorded neutron exposures, they were included in the NDRP, and therefore 

in the SEC. Ms. Ruttenber again confirmed that the neutron dosimetry data in the Ruttenber 

database came from the records maintained by the Rocky Flats site via the staff of the NDRP. 

Dr. Ulsh therefore again concluded that since the data for the Ruttenber database and the NDRP 
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6

came from the same source, there should be minimal discrepancies between the two, but they 

agreed to test this. 

On June 20, 2008, Margaret Ruttenber provided NIOSH a list of workers from the Ruttenber 

database whom she believed had positive neutron exposure, but were stationed in buildings other 

than those included in the RFP SEC petition. NIOSH discovered some problems with this list (it 

included individuals who did not appear to meet the agreed criteria) that reinforced the need to 

collaborate to generate the lists, so that everyone involved could agree that the query had 

captured the group of workers of interest. 

On July 8, 2008, Margaret Ruttenber provided a second list of workers from the Ruttenber 

database whom she believed had positive neutron exposure, but were stationed in buildings other 

than those included in the RFP SEC petition. This second list contained several columns of data 

for which no definition was provided, and it was unclear how the numbers were calculated, 

therefore NIOSH again requested an interpretation of the data included in this list. 

On July 29, 2008, Margaret Ruttenber provided an interpretation of the data in her second list via 

email. She again indicated her agreement that it would be beneficial for NIOSH to come back to 

visit. The purpose of this trip would be to compare the NDRP with the Ruttenber data, and to 

take possession of the Ruttenber data. 

Following resolution of legal issues surrounding transfer of the Ruttenber data to NIOSH, on 

February 9, 2009, Dr. Ulsh, along with ABRWH member Mark Griffon and Mutty Sharfi of the 

ORAU Team, visited Margaret Ruttenber. Ms. Ruttenber made a presentation on the data and 

studies, and gave NIOSH a copy of the database containing measured and imputed neutron 

dosimetry, and some attendant documentation. In discussions during this visit, it was once again 

confirmed that the actual dosimetry data used in the Ruttenber studies were provided by the 

Rocky Flats site, and were the same dosimetry data used by the NDRP. It was further discussed 

that the interviews conducted by the Ruttenbers with former Rocky Flats workers consisted of 

discussions with a limited number of individuals with experience in plant operations on the topic 

of job titles and their potential exposures to radiation and numerous toxic chemicals of interest. 

II. Data Sources

Throughout the deliberative process related to the RFP SEC petition, and especially after the 

SEC classes were established, it has been repeatedly claimed that the Ruttenber studies provide a 

separate source of data, distinct from the NDRP. It has been further suggested that the Ruttenber 

studies should be used as a basis for including workers in the SEC class. 

As discussed below, this idea that the Ruttenber studies and the NDRP are separate and distinct 

sources of data is inaccurate. Both the NDRP and the Ruttenber studies relied on the same 

source data – namely, the dosimetry records provided by the Rocky Flats radiation protection 

department. 

NDRP 
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The NDRP Protocol [28] describes the first source of the dosimetry data used in the study as the 

neutron dosimetry records: 

“There were two primary information sources that were used to identify workers affected by 

the NDRP. The most directly related source was the neutron dosimetry worksheets. These 

sheets specifically identified those workers who were assigned neutron-sensitive elements 

(i.e., neutron films or glass plates).” 

In addition to those workers directly monitored for neutrons, a broader net was cast for workers 

who should be included in the NDRP. These workers were identified through records of the 

beta-gamma worksheets filled out upon reading beta-gamma films workers wore in plutonium 

buildings: 

“The second source of names was the beta-gamma worksheets for plutonium-related 

buildings. Only the beta-gamma worksheets from the plutonium production buildings (any 

building with a number starting with 7) and Buildings 91 and 86, and the combined 

worksheets for Buildings 21, 22, and 23, were entered into the beta-gamma database. The 

rosters on the beta-gamma worksheets for these buildings were used to identify workers who 

would be assigned a notional neutron dose if they were not monitored for neutrons. Betagamma worksheets for other buildings were not entered into the database.” [28] 

Concern has been expressed especially about whether “roving” workers were adequately 

accounted for in the NDRP. “Roving” workers were those officially stationed in a non-neutron 

building, but whose work occasionally took them into neutron buildings; therefore they had the 

potential to be exposed to neutrons. As described in the NDRP protocol, and as explained by 

NIOSH, these workers are explicitly included in the NDRP, and therefore the SEC classes: 

“A small portion of the total number of neutron worksheets represent[s] the issuance of 

neutron dosimeters to a few personnel whose home building assignment was a nonplutonium 

production building, such as Buildings 21, 22, 23, 34, 44, 81, and 86. These individuals 

primarily worked in non-neutron buildings but were routinely issued neutron dosimeters 

because they occasionally performed work activities in plutonium production buildings. 

Some examples of these job descriptions are guards, radiation monitors, technical 

researchers, and uranium process operators.” [28] 

It should be noted that the data used by the NDRP are primary dosimetry records created upon 

reading the films. This contrasts with the derivative data contained in electronic databases upon 

transcription of the primary records. In general, there is nothing inherently deficient about 

derivative databases if the data are entered reliably and correctly. Indeed, this is the type of data 

most typically available to NIOSH for dose reconstruction. However, when primary data are 

available and usable, they generally take precedence over derivative data, and certainly are 

considered more reliable than estimated or imputed dosimetry data. Since the Ruttenber studies 

relied upon imputed neutron dose estimates, it would be difficult to make the case that the 
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8

estimates calculated for the Ruttenber studies should take precedence over the actual dosimetry 

results (including the re-reading of over 90,000 original neutron films) used by the NDRP. 

Ruttenber studies 

The CDPHE team constructed their study cohort using Rocky Flats records retrieved from a 

number of sources, including Los Alamos National Laboratory: 

“A database was acquired from LANL that had been maintained for 9,539 production 

workers who were ever employed at Rocky Flats between 1951 and 1979. This database was 

originally constructed for the epidemiologic studies of Wilkinson et al. (1987). LANL had 

updated the vital status for this group through 1993, and had retrieved and coded death 

certificates for the deceased. This database contained name, maiden name, employee 

identification number (EID), dates of birth, hire, termination, and death, the date a person 

was last known to be alive, state of birth, and underlying cause of death coded according to 

the International Classification of diseases, 9th Revision (ICD-9). This database was reported 

to be relatively accurate and all fields except the date of death were used in construction of 

the cohort database.” [23] 

For its report [23], the CDPHE obtained employment records directly from the Rocky Flats 

Personnel Offices. This report provides the following: 

“Records for 14,327 former or current workers were obtained from the RFETS Personnel 

Offices. This file contained name, EID, social security number (SSN), dates of birth, hire, 

termination and death, last job title, and last-known home address. These data were reported 

to be of reasonable quality and all fields, except date of death (which was not reliable 

according to RFETS personnel), were used in construction of the production-era cohort 

database. 

The nine databases that compose the Radiological Health Records System (RHRS) were 

obtained from the RFETS Radiation Protection Division. These databases were used both to 

identify workers for inclusion in the production era database and to link dosimetry data to 

individual workers. Three of these databases contained personnel information, including 

name, person-ID, SSN, date of birth, sex, last known address, telephone number, dates of 

hire and termination. Person-ID is a unique personal identification code that was reportedly 

assigned only once to each employee. This identification code was useful because other 

personal identifiers such as SSN and EID were sometimes shared by married couples, were 

assigned to more than one worker, or were inaccurately recorded. Person-ID was the unique 

identifier used to link personnel data to the radiation databases. The RHRS databases were 

considered to be of good quality and all fields were used in construction of the production era 

database.” (page 11) 

“In 2000, we matched the cohort database with the radiation dosimetry database maintained 

by the Radiation Protection Division at RFETS and identified a group of 2,448 productionera workers who were not in the cohort database. These workers had been monitored for 

radiation exposure, but were not listed in any of the other databases developed for our study. 
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9

The group is composed of contractors and Department of Energy employees who performed 

tasks that placed them at risk for internal and external radiation exposures; for this reason 

they were added to the production era database.” (page 12) 

“Although no historical data exist regarding the specific job tasks performed by contractors, 

both internal and external radiation dose data exist for most of the contractors.” (page 12) 

It was recommended to the CDPHE team that their dose estimates rely on existing dosimetry 

data, as described in their study protocol: 

“The DWG [Dosimetry Working Group] also supported the use of existing external dose data 

for epidemiologic studies, because they are the best available estimates of doses from 

external exposures. They suggested, however, that the records for cumulative external doses 

be corrected for possible errors in neutron dose estimates.” [29] 

The CDPHE team acted on this recommendation, and proceeded to obtain dosimetry records 

from Rocky Flats. The report states as follows [23]: 

“Data for external radiation doses came from film and thermoluminescent dosimetry (TLD) 

badges that measured total body doses from external gamma and neutron exposures. Six 

separate radiation databases were obtained from the Radiation Protection Division at Rocky 

Flats. Two databases recorded the external doses measured by personal dosimeters. The first 

contained quarterly doses recorded from 1991 to 1996 and the second, combined annual 

doses recorded for individual workers for all exposures occurring before December 31, 1976 

and doses for individual workers recorded for variable time periods from January 1, 1977 

through December 31, 1990.” (page 12) 

 

“Data for annual external radiation doses were also obtained from LANL for the cohort of 

9,539 workers that was established by Wilkinson et al. (1987). These data were compared 

with data from other sources for quality assurance, and used when external doses were 

missing from other sources.” (page 13) 

A challenge the CDPHE team faced was that for some time periods, doses from both neutrons 

and gamma were combined into one total penetrating dose number. 

“The electronic databases recorded separate doses from gamma photons and neutrons for 

1959-1963 and for all years after 1975. For 1952-1958 and 1964-1975, only total penetrating 

dose–the sum of equivalent doses from gamma photons and neutrons–was recorded 

electronically.” [23] 

Since there were questions about the reliability of the original neutron dose estimates, the 

CDPHE team had to develop methodologies to split this total penetrating number back into the 

gamma and neutron components. As noted earlier, the CDPHE team would have preferred to 

rely on the results from the NDRP; however the NDRP was not at a point where revised neutron 

dosimetry estimates were available. On consultation with Roger Falk (who was also conducting 
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10

the NDRP), the CDPHE team devised a strategy to split the total penetrating dose into gamma 

and neutron components based on job category and work location; this strategy is described in 

the next section. 

III. Neutron dose estimate methodologies

While the source dosimetry data used by both the Ruttenber studies and the NDRP are the same, 

there are some differences in how these data are used to calculate neutron doses. The Ruttenber 

team recognized that it would have been preferable to use the results of the NDRP; however 

these were unavailable. The following section describes how the Ruttenber team calculated 

neutron doses, and how the NDRP later calculated neutron doses. 

Neutron dose reconstruction project 

There are multiple components to the doses calculated in the NDRP. The first component was 

the re-evaluated neutron films worn by the individual workers. The NDRP re-evaluated over 

90,000 films. The second component was notional doses, which the NDRP defined as follows: 

“Notional neutron doses are neutron doses that were assigned for periods of time identified as 

gaps in the worker’s neutron dose timeline.” [28] 

The term “gap” was also defined in the NDRP Protocol: 

“A gap is defined as a period of time when the worker was not monitored for neutrons or has 

no recorded dose of neutrons but was monitored for gamma doses in a plutonium related 

building for that period.” [28] 

Buildings with significant neutron potential included: 707, 771, 776, 777, 778, 779, 886, and 

991. Some workers from a few other buildings (21, 22, 23, 34, 44, 81, and 86) were included if 

they were monitored for either neutrons or for beta-gamma exposures in a neutron building. 

“The period of the gap was determined from the neutron work-sheet timeline. If more than 

one building was involved in the period of the gap, determined from the header information 

on the gamma worksheets for the period of the gap, the gap was divided into segments based 

on the dates on the gamma worksheets.” [28] 

The NDRP methodology made maximum use of an individual’s own dosimetry data to calculate 

notional doses to cover gaps. The more dosimetry data a worker had (and hence the smaller the 

gap period), the more heavily his own data weighed in the notional dose calculation. This is the 

most reliable method for calculating notional doses, as it minimizes the application of population 

properties to individuals. 

Ruttenber studies 
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It was recognized that there were problems with the neutron dose calculations originally 

performed by the site in the 1950s and 1960s; this was the motivation for conducting the NDRP 

in the first place [29]: 

“Neutron doses have not been accurately measured for workers during the early years of RF 

operations. Although the Health Effects Department has initiated a program to reconstruct 

neutron doses for all current employees, these data may not be available for a number of 

years. Therefore, we will determine the feasibility of using data from the JEM to identify 

those Job titles, years of employment, and buildings that would be indicative of possible 

neutron exposure and use these to develop a dichotomous variable (exposed not exposed) for 

exposure status to assign to subjects in the cohort mortality study and then make detailed 

neutron dose reconstructions for the subjects in the case cohort studies.” 

It should be noted that in the absence of individual neutron dosimetry records, the use of a job 

exposure matrix (JEM) by the Ruttenber team led to the assignment of neutron dose to all

members of a job class if any member of that job class could have been exposed to neutrons. 

From an epidemiological standpoint, this is most likely of little consequence since it only affects 

how the total recorded penetrating dose is subdivided into neutron and gamma components. 

However, it can have dramatic consequences for constructing a list of individuals who might 

have been exposed to neutrons. 

In the 1990s, there was considerable overlap in the NDRP and the Ruttenbers’ epidemiological 

studies [29]: 

“The RF Health Effects Department has already begun a program to recalculate neutron 

doses for all workers who are still employed at RF. We will work with them to develop a 

plan to re-estimate neutron doses for subjects in our studies by counting neutron tracks on old 

neutron films. This effort may not be completed in time for the epidemiologic studies. If this 

is the case, we will use the JEM to help identify subjects who had neutron exposures and to 

develop a simple categorical scale based on any vs. no exposure, for instance. 

We will use the JEM to identify the processes and locations that exposed individuals to high 

neutron doses (such as working around fluorinators), and then job titles will be classified 

according to whether work was performed near those processes and locations. To do this, 

floor plans of the buildings will be obtained and the sites of process lines and equipment 

identified, Floor plans with process lines and measurements for gamma and neutron doses are 

available in records of Radiation Protection Division gamma and neutron surveys for some 

years. Also, we will identify the job duties associated with each job title, and determine 

whether workers tended to work in one place or if they rotated through different locations.” 

The Ruttenber team recognized that the best option for calculating neutron doses would be to use 

the NDRP results; however these were unavailable [29]: 

“Although it would be preferable to re-evaluate external and internal radiation doses for all 

RF workers, this effort would take a number of years to complete and would be costly. 
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12

Instead, we will take the following steps in estimating radiation doses for the cohort mortality 

study...” 

Given that completion of the NDRP was still a number of years away in the mid- to late 1990s, 

the Ruttenber team had to devise a method for splitting combined penetrating doses into the 

neutron and gamma components. Upon consultation with the NDRP staff, the Ruttenber team 

applied rules of thumb based on building and job title to make this split. The split was 

accomplished by applying ratios and using a job-exposure matrix. It is important to note that this 

method is superior to many other epidemiological studies, in that it does make use of the 

individual’s own penetrating dose measurements. However, properties of a group (i.e., job 

category) are applied to split this number into neutron and gamma components [23]. 

“Because computer databases for dosimetry have recorded total penetrating doses (the sum of 

equivalent doses from gamma photons and neutrons) for most workers between 1952 and 

1975, it is not possible to directly extract the erroneous neutron doses from the electronic 

data for these workers. There are electronic records with separate gamma and neutron doses 

for some workers from 1952 to 1970. Analyses of ratios for accurate gamma and neutron 

doses between 1968 and 1971 indicate that neutron doses for Building 771 (the site of 

plutonium fluorination processes) were about two times as high as gamma doses for the years 

between 1952 and 1966, and one-half as high as gamma doses for the other buildings where 

neutron exposures occurred during this time period. We used these ratios and data on 

administrative building assignments and job titles to adjust neutron doses for workers with 

separate neutron and gamma doses. 

We used these adjusted neutron doses and presumably correct neutron doses from 1977 

to 1989 to estimate “correction ratios” for total penetrating doses–the ratios of neutronadjusted total penetrating dose to total penetrating dose for all workers with recorded neutron 

doses for building 771 (mean of ratios = 1.99, standard deviation [SD] = 0.92), and for other 

buildings (mean of ratios = 1.13, SD = 0.82). We then used the neutron dose data and the 

JEM to identify all buildings that had neutron exposures, and computed corrected total 

penetrating doses by applying the correction ratios to total penetrating dose for the workers in 

these buildings who did not have separate neutron doses recorded for the years 1952 to 

1966.” (page 13-14) 

While the source dosimetry data used by both the NDRP and by the Ruttenbers’ epidemiological 

studies were the same, the methods used to calculate neutron doses in the absence of direct 

neutron dosimetry differed. This was a result of the NDRP not being finished in time for the 

Ruttenber team to use. When compared to the dose estimate methods used in a typical 

epidemiological study, the method used by the Ruttenber team is quite preferable in that it is at 

least based on each individual’s total penetrating dose data. However, since some degree of 

imputation based on population properties is necessary to split the penetrating dose into gamma 

and neutron doses, it was recognized, even by the Ruttenber team, that the method employed by 

the NDRP (direct re-reading of original neutron films) was preferable. It is not scientifically 

justifiable to give precedence to imputed results over direct neutron dosimetry, regardless of the 

sophistication of the methodology used to calculate the imputed numbers. 
NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 

USC §552a and has been cleared for distribution. 

13

IV. Comparison of Ruttenber database and NDRP

There are several fields in the Ruttenber database that contain what appear to be neutron doses. 

These include: RECORD_NEU, NEU_RECPEN, NEU_NEW_ADJPEN2, and NEU_ADJPEN3. 

NIOSH has made multiple attempts to determine the final neutron dose assigned in the Ruttenber 

database through communications with Margaret Ruttenber. In an email dated May 20, 2009, 

Ms. Ruttenber stated: 

“Based on Roger Falk's protocol for building 771 we used the ratio as follows: 

BLDG = 771, 

ADJ_PEN = 2.0* IMP_PEN, 

ADJ_NEUT=(2/3)*ADJ_PEN 

ADJ_GAMP=(1/3)*ADJ_PEN 

For all other BLDG’s, 

ADJ_PEN = 1.1* IMP_PEN, 

ADJ_NEUT=(1/3)*ADJ_PEN 

ADJ_GAMP=(2/3)*ADJ_PEN 

So based on those ratios the Recorded Pen dose pre 1966 would be multiplied by .666 or 

.333 depending on the building.” 

In a follow-up email dated May 20, 2009, NIOSH requested clarification of the definitions of the 

NEU_NEW_ADJPEN2, NEU_ADJPEN3, and IMP_PEN fields, but received no reply. Followup telephone messages were also unreturned. Since we were unable to determine exactly which 

field contains the neutron dose applied by the CDPHE team, we took the most expansive view 

and treated any individual with a nonzero value in RECORD_NEU, NEU_RECPEN, 

NEU_NEW_ADJPEN2, and NEU_ADJPEN3 as neutron-exposed according to the CDPHE 

studies. Using these most-inclusive criteria results in a total of 4,163 RFP workers with positive 

values in these fields prior to 1967 that have no pre-1967 measured or notional neutron dose in 

the NDRP. Interestingly, there are also 486 individuals listed in the NDRP who are not included 

in the Ruttenber database; NIOSH has no explanation for this. The assignment of neutron dose 

to 4,163 additional workers is a direct result of the CDPHE team not having access to the 

original neutron dosimetry records, and the consequent decision to apply neutron dose based on 

job classes. If any member of a particular job class could have been neutron exposed, then all 

workers in that job class were assigned neutron dose. 

Press reports have suggested that use of the Ruttenber data would result in the addition of several 

thousand people to the SEC class. However, the simple fact that the workers were assigned 

neutron dose in the Ruttenber database would not be sufficient to merit addition to the SEC 

because there are multiple criteria required by law for membership in the SEC (e.g., at least 250 

days of employment in an SEC period, having a presumptive cancer). As well as criteria applied 

by DOL to determine whether or not individuals meet the SEC class definition (e.g., having a 

neutron dose equal to or greater than 100 mrem per year, thereby meeting the requirement that an 
NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 

USC §552a and has been cleared for distribution. 

14

individual was or should have been monitored for neutrons by current standards). In addition, 

numerous claimants with no evidence of neutron exposure have already been added to the SEC 

based on their work in Building 81. 

To determine the true impact of the use of the Ruttenber data to determine SEC eligibility, 

NIOSH performed a more detailed analysis of the data using claimant data as comparison. For 

those claimants who are not already in the SEC class but assigned neutron dose by the CDPHE 

team, we also examined whether there was any indication of neutron exposure potential in 

workers’ radiation records. These indications could include neutron dosimetry results, records of 

work in plutonium buildings, reports of incidents which occurred in plutonium buildings, 

plutonium bioassay results, or lung counts indicating actual or suspected plutonium exposures. 

There are a total of 100 current claims for RFP workers who are not included in the NDRP prior 

to 1967, but for whom the Ruttenber team imputed pre-1967 neutron doses. Of these 100 claims, 

50 individuals are already included in the SEC class, 22 had non-SEC cancers, nine had less than 

250 days of employment in the SEC period, four had dose reconstructions with a POC>50%, 

three individuals’ claims were closed because either the employee died with no survivors or the 

survivors died, and one had a non-SEC cancer but was compensated for beryllium exposure. 

Thus, for a total of 89 of the 100 claimants with the imputed neutron doses in the Ruttenber 

database, this data can have no impact on the compensation decision. In addition, the imputed 

annual neutron doses in the Ruttenber database are less than 100 mrem for each year in the SEC 

period for 10 of the remaining 11 individuals. A detailed review of these claimants’ dosimetry 

files was conducted and there is nothing that suggests neutron exposure prior to 1967. That is, 

there were no neutron dosimetry results, incident reports from a Pu building, Pu bioassay results, 

or any other evidence indicative of neutron exposure potential. There is one claimant with an 

annual neutron dose greater than 100 mrem in the Ruttenber database, but not in the NDRP. 

There is no evidence of neutron exposure potential for this individual in his dosimetry files. 

DOL is responsible for determining whether such evidence is sufficient to add individuals to the 

SEC. Therefore, with the possible exception of the aforementioned claimant, the use of the 

Ruttenber database in addition to the information already used by DOL would result in no 

additional members to the SEC. There is every reason to believe that this general pattern 

observed among RFP claimants based on the Ruttenber data would be reflected in the RFP 

worker population at large. This demonstrates that press suggestions that upwards of 3,000 RFP 

workers would be added to the SEC by use of the Ruttenber database are unsubstantiated. 

V. Conclusion

This paper analyzed and compared the methodologies used by two studies, the Ruttenber 

epidemiological studies and the Neutron Dose Reconstruction Project (NDRP), to estimate 

neutron doses to Rocky Flats workers during the time period of the two established SEC classes 

(April 1, 1952 to December 31, 1966). The results of this analysis are: 

 The idea presented in the press that these studies rely on different records is a 

misconception. Both the Ruttenber and NDRP studies started from the dosimetry records 

provided by the radiation protection staff at the Rocky Flats site. 

 While the CDPHE team clearly expressed their preference to use the NDRP results, these 

results were not available to the CDPHE team when they were performing their 
NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 

USC §552a and has been cleared for distribution. 

15

epidemiological studies. In the absence of the NDRP results, the CDPHE team had to 

devise a strategy for splitting total penetrating doses into gamma and neutron dose 

components. 

 The method devised by the CDPHE team involved determining which buildings 

contained neutron source terms that could lead to neutron exposures, and determining 

which job types could have been exposed in those buildings. There is no disagreement 

between the Ruttenber studies and the NDRP regarding which buildings were “neutron” 

buildings. 

 The CDPHE team assigned neutron doses to all members of a job type if any member of 

that job type could have been exposed to neutrons. The NDRP relied on primary 

dosimetry records, constructed detailed individual worker history timelines, and assigned 

neutron doses to workers if there was evidence of neutron exposure potential in the form 

of either neutron or beta/gamma monitoring in a neutron building. This difference in 

methodology led the Ruttenber studies to assign neutron doses to 4,163 more RFP 

workers than did the NDRP. There are also 486 individuals listed in the NDRP who are 

not included in the Ruttenber database; NIOSH has no explanation for this. 

 NIOSH determined the impact of using the Ruttenber database in addition to the NDRP 

for determining eligibility for inclusion in the SEC, should a decision be made to do so 

by DOL. This determination involved a detailed review of the 100 current claims for 

which the Ruttenber studies, but not the NDRP, assigned neutron dose prior to 1967. 

There was no evidence in any of the dosimetry records associated with these claims to 

suggest that any of these workers was exposed to neutrons. 

 Out of the 100 current claims examined in detail, with the exception of one possible 

claimant, no additional workers would meet the SEC criteria if the Ruttenber database 

was used to determine SEC eligibility. Claims in the press that thousands of additional 

workers would be compensated are unsubstantiated. 

A copy of this report has been provided to the Department of Labor to inform its decision 

whether or not to use the Ruttenber data for determining SEC eligibility. 
NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 

USC §552a and has been cleared for distribution. 

16

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NOTICE: This report has been reviewed to identify and redact any information that is protected by the Privacy Act 5 

USC §552a and has been cleared for distribution. 

17

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USC §552a and has been cleared for distribution. 

18

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